U.S. patent application number 14/367136 was filed with the patent office on 2014-11-13 for abrasive material regeneration method and regenerated abrasive material.
This patent application is currently assigned to KONICA MINOLTA, INC.. The applicant listed for this patent is KONICA MINOLTA, INC.. Invention is credited to Akihiro Maezawa, Yuuki Nagai, Atsushi Takahashi.
Application Number | 20140331567 14/367136 |
Document ID | / |
Family ID | 48668298 |
Filed Date | 2014-11-13 |
United States Patent
Application |
20140331567 |
Kind Code |
A1 |
Takahashi; Atsushi ; et
al. |
November 13, 2014 |
Abrasive Material Regeneration Method And Regenerated Abrasive
Material
Abstract
Abrasive material regeneration method regenerates a cerium oxide
abrasive material from a used abrasive material slurry containing
the cerium oxide abrasive material and resulting from grinding a
grinding subject having silicon as the primary component,
characterized by regenerating the abrasive material containing
cerium oxide through: a slurry recovery step (A) for recovering an
abrasive material slurry discharged from a grinder; an
isolation/concentration step (B) for adding a magnesium salt as an
inorganic salt to the recovered abrasive material slurry,
aggregating the abrasive material under the condition that the pH
value of the mother liquor converted to 25 DEG C is at least 6.5
and less than 10.0, and thus isolating and concentrating the
abrasive material from the mother liquor; and an abrasive material
recovery step (C) for recovering the isolated and concentrated
abrasive material.
Inventors: |
Takahashi; Atsushi;
(Hachioji-shi, JP) ; Nagai; Yuuki; (Tachikawa-chi,
JP) ; Maezawa; Akihiro; (Hino-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KONICA MINOLTA, INC. |
Chiyoda-ku, Tokyo |
|
JP |
|
|
Assignee: |
KONICA MINOLTA, INC.
Chiyoda-ku, Tokyo
JP
|
Family ID: |
48668298 |
Appl. No.: |
14/367136 |
Filed: |
December 5, 2012 |
PCT Filed: |
December 5, 2012 |
PCT NO: |
PCT/JP2012/081463 |
371 Date: |
June 19, 2014 |
Current U.S.
Class: |
51/298 ;
51/309 |
Current CPC
Class: |
B28D 5/007 20130101;
C02F 1/5236 20130101; C02F 1/66 20130101; Y02P 70/179 20151101;
C02F 2103/346 20130101; C02F 2101/10 20130101; B24B 57/00 20130101;
C09K 3/1409 20130101; B24B 57/02 20130101; Y02P 70/10 20151101;
C02F 2103/12 20130101 |
Class at
Publication: |
51/298 ;
51/309 |
International
Class: |
C09K 3/14 20060101
C09K003/14; B24B 57/00 20060101 B24B057/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 2011 |
JP |
2011-282037 |
Dec 22, 2011 |
JP |
2011-282041 |
Claims
1. A method for regenerating a cerium oxide-containing abrasive
from a used abrasive-containing slurry that was used in polishing
an object mainly composed of silicon, the method comprising: (A)
collecting an abrasive-containing slurry discharged from an
abrasive device; (B) separating the abrasive from a mother liquid
and concentrating the abrasive by adding a magnesium salt as an
inorganic salt to the collected abrasive-containing slurry and
aggregating the abrasive at a converted pH ranging from 6.5 to less
than 10.0 of the mother liquid at 25.degree. C.; and (C) collecting
the separated and concentrated abrasive.
2. The method of claim 1, further comprising: (D) adjusting sizes
of particles of the collected abrasive.
3. The method of claim 1 or 2, wherein a first abrasive-containing
slurry that contains washing water and a second abrasive-containing
slurry that was used are collected in the step (A).
4. The method of claim 3, wherein the first abrasive-containing
slurry and the second abrasive-containing slurry collected in the
step (A) are mixed before the steps (B) and (C).
5. The method of claim 3, wherein the first abrasive-containing
slurry and the second abrasive-containing slurry collected in the
step (A) are separately subjected to the steps (B) and (C).
6. The method of claim 2, wherein in the step (C), the collecting
is conducted through separation by decantation utilizing
spontaneous sedimentation.
7. The method of claim 2, wherein in the step (D), a dispersing
agent is added to a liquid of the collected abrasive, and
thereafter dispersion is conducted using an ultrasonic disperser or
a bead mill disperser to control the sizes of the particles of the
regenerated abrasive.
8. The method of claim 7, wherein the disperser used in the step
(D) is the ultrasonic disperser.
9. The method of claim 7, wherein the dispersing agent is composed
of a poly-carboxylic acid-based polymer.
10. A regenerated abrasive produced by the method of claim 1.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for regenerating
an abrasive through collecting cerium oxide from a used cerium
oxide-containing abrasive to reuse the collected cerium oxide as a
regenerated cerium oxide-containing abrasive, and an abrasive
regenerated through the method.
BACKGROUND ART
[0002] As an abrasive for finely polishing an object (e.g., an
optical glass, a glass substrate for an information storage medium
and a semiconductor silicon substrate) in a finishing process, a
rare-earth oxide material mainly composed of cerium oxide and
further containing lanthanum oxide, neodymium oxide and/or
praseodymium oxide has been used.
[0003] Normally, the rare-earth element which is a main component
of an abrasive, especially cerium oxide, relies on imported
minerals because this element is obtained from a mineral that is
not produced in Japan. A cerium oxide-containing abrasive is
composed of fine particles with high degree of hardness and thus
important for uses as an optical abrasive for electronic components
such as optical lens, semiconductor silicone substrates and glass
plates of liquid crystal displays. An abrasive for optical abrasion
contains the above-mentioned cerium oxide, and may further contain
a metal element (s) such as sodium and chromium and/or a rare-earth
element(s) such as yttrium and dysprosium. Thus, an abrasive for
optical abrasion is strictly inhibited from being simply disposed
in view of environmental pollution. A waste liquid that contains
cerium oxide used in polishing is therefore strongly desired to be
made non-polluting. Hence, techniques to reuse a resource (s) in a
waste liquid of an optical abrasive containing cerium oxide are
important also in terms of making a non-polluting liquid.
[0004] In various fields of industry, a conventional method for
disposing a waste liquid that contains suspended particles normally
includes aggregating and separating the suspended particles using a
neutralizer, inorganic coagulant or polymeric coagulant,
discharging a treated liquid and disposing the aggregated and
separated sludge.
[0005] A cerium-oxide abrasive is used in large quantity in a
polishing process, and its waste liquid also contains a
component(s) derived from the polished object (e.g., debris of a
polished optical glass). In addition, it is difficult to
efficiently separate the abrasive from the component (s) derived
from the polished object. Because a waste liquid is disposed after
use at present as described above, there are problems concerning
environmental burdens and disposal cost.
[0006] Thus, it has been important to establish a method for
efficiently collecting a main component of an abrasive for
recycling the rare-earth element which is a scarce material.
[0007] As a method for collecting an abrasive component, Patent
Document 1 discloses a solid-liquid separation method including
adding an electrolyte is to a used abrasive liquid that contains a
cerium oxide-based abrasive for polishing a glass, and maintaining
the abrasive liquid temperature at 25.degree. C. for 2 hours to
dissolve a component (s) derived from a polished substrate (Si
component or Al component), and separate the abrasive and let the
abrasive settle out. In a method described in Patent Document 1, an
alkali metal hydroxide, alkali metal carbonate, alkali metal salt
and ammonium salt are used as the electrolyte.
[0008] Patent Document 2 discloses a method including adding poly
aluminum chloride and a coagulant composed of a polymer to a used
abrasive liquid that contains an abrasive mainly composed of cerium
oxide to aggregate a solid component of the used abrasive,
performing anhydration to obtain a dehydrated cake of the waste
abrasive, mixing the waste abrasive with an aqueous sodium
hydroxide or aqueous potassium hydroxide to dissolve a
water-soluble impurity(ies), and collecting the abrasive by
solid-liquid separation. Patent Document 3 discloses a method
including adding sulfuric acid to a used abrasive, applying heat
thereto, dissolving a rare-earth element or rare metal, and
separating and removing an aggregate of silica etc. in the
slurry.
[0009] Patent Document 4 discloses a method for collecting a
colloidal silica-based abrasive, the method including conducting
solid-liquid separation by addition of an alkali to a chemical
mechanical polishing (CMP) waste liquid in the presence of a
magnesium ion to adjust pH to 10 or higher and cause aggregation,
adjusting the pH of the solid component in a pH adjusting tank to 9
or lower to elute the magnesium ion, and collecting the abrasive.
Non-Patent Document 1 is a review article regarding the
above-described metal-collecting methods.
[0010] However, the above methods disclosed by Patent Documents 1
to 4 provide a collected abrasive of insufficient purity. Such a
collected abrasive is not suitable for fine polishing.
[0011] In the method of Patent Document 4, if an abrasive mainly
composed of cerium oxide is used in polishing an object mainly
composed of silicon such as a glass, addition of an additive such
as magnesium chloride to an abrasive-containing slurry that
contains a used abrasive at a pH of 10 causes co-aggregation of an
abrasive component and a glass component, which lowers the purity
of an obtained regenerated abrasive. This is because when the pH is
over 10, a component (s) derived from a polished object mainly
composed of silicon (e.g., glass) become easier to aggregate than
the abrasive component upon addition of an additive.
[0012] Patent Document 5 discloses a method for producing a
regenerated cerium oxide-containing abrasive by freezing a
collected used liquid to regenerate a secondary particles of cerium
oxide followed by removal of water. However, the method of Patent
Document 5 requires a huge facilities for conducting the freezing
and thus requires enormous initial investment.
PRIOR ART DOCUMENT
Patent Document
[0013] Patent Document 1: Japanese Patent Application Laid-Open
Publication No. Hei06-254764 [0014] Patent Document 2: Japanese
Patent Application Laid-Open Publication No. Hei11-90825 [0015]
Patent Document 3: Japanese Patent Application Laid-Open
Publication No. Hei11-50168 [0016] Patent Document 4: Japanese
Patent Application Laid-Open Publication No. 2000-254659 [0017]
Patent Document 5: Japanese Patent Application Laid-Open
Publication No. 2010-214515
Non-Patent Document
[0017] [0018] Non-Patent Document 1: Kinzoku-Shigen Report (Report
regarding metal resources) p. 45, November 2010.
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0019] The present invention is made in view of the above-described
problems to provide a method for regenerating an abrasive, the
method including efficiently collecting cerium oxide from a used
abrasive mainly composed of cerium oxide and obtaining a
regenerated abrasive in a simple manner, and a regenerated
abrasive.
Means for Solving Problems
[0020] The present inventors have earnestly studied given the above
problems, and found that a method for regenerating an abrasive
through efficiently collecting cerium oxide from a used abrasive
mainly composed of cerium oxide and obtaining a regenerated
abrasive in a simple manner can be realized as a method for
regenerating a cerium oxide-containing abrasive from a used
abrasive that contains cerium oxide, the method including: (A)
collecting an abrasive-containing slurry discharged from an
abrasive device; (B) separating and concentrating the abrasive from
a mother liquid, utilizing the difference of their specific
weights, by adding a magnesium salt which is a divalent alkali
earth metal salt as an inorganic salt to the collected
abrasive-containing slurry and aggregating the abrasive under the
condition that aggregates the abrasive selectively and does not
aggregate debris derived from a polished object such as silica
particles derived from a polished optical glass; and (C) collecting
the separated and concentrated abrasive. The present invention is
thus made.
[0021] That is, the above object of the present invention is
accomplished by the following ways.
[0022] 1. A method for regenerating a cerium oxide-containing
abrasive from a used abrasive slurry that contains the abrasive and
was used in polishing an object mainly composed of silicon, the
method including:
[0023] (A) collecting an abrasive-containing slurry discharged from
an abrasive device;
[0024] (B) separating the abrasive from a mother liquid and
concentrating the abrasive by adding a magnesium salt as an
inorganic salt to the collected abrasive-containing slurry and
aggregating the abrasive at a converted pH ranging from 6.5 to less
than 10.0 of the mother liquid at 25.degree. C.; and
[0025] (C) collecting the separated and concentrated abrasive.
[0026] 2. The method of the item 1, further including:
[0027] (D) adjusting sizes of particles of the collected
abrasive.
[0028] 3. The method of the item 1 or 2, wherein
[0029] a first abrasive-containing slurry that contains washing
water and a second abrasive-containing slurry that was used are
collected in the step (A).
[0030] 4. The method of the item 3, wherein
[0031] the first abrasive-containing slurry and the second
abrasive-containing slurry collected in the step (A) are mixed
before the steps (B) and (C).
[0032] 5. The method of the item 3, wherein
[0033] the first abrasive-containing slurry and the second
abrasive-containing slurry collected in the step (A) are separately
subjected to the steps (B) and (C).
[0034] 6. The method of any one of the items 2 to 5, wherein
[0035] in the step (C), the collecting is conducted through
separation by decantation utilizing spontaneous sedimentation.
[0036] 7. The method of any one of the items 1 to 6, wherein
[0037] in the step (D), a dispersing agent is added to a liquid of
the collected abrasive, and thereafter dispersion is conducted
using an ultrasonic disperser or a bead mill disperser to control
the sizes of the particles of the regenerated abrasive.
[0038] 8. The method of the item 7, wherein
[0039] the disperser used in the step (D) is the ultrasonic
disperser.
[0040] 9. The method of the item 7 or 8, wherein
[0041] the dispersing agent is composed of a poly-carboxylic
acid-based polymer.
[0042] 10. A regenerated abrasive produced by the method of any one
of the items 1 to 9.
Effects of the Invention
[0043] By virtue of the above ways of o the present invention,
there is provided a method for regenerating an abrasive through
efficiently collecting cerium oxide from a used abrasive mainly
composed of cerium oxide and obtaining a regenerated abrasive in a
simple manner, and a regenerated abrasive.
[0044] The mechanisms of the above effect of the present invention
are not fully and definitively revealed, but the following
reasoning can be made.
[0045] The effect of the present invention is characterized in that
the method for selectively collecting cerium oxide which is a main
component of an abrasive from the used abrasive-containing slurry
in high concentration enables not only collection of cerium oxide
but also collection of the abrasive in high concentration and easy
regeneration of the collected abrasive.
[0046] The technical idea is utilizing a presumable specific
interaction between cerium oxide and the inorganic salt, namely, a
magnesium salt which is a divalent alkali earth metal salt. It is
common to add a coagulant having high specific weight to a used
abrasive to separate the used abrasive as a solid component,
followed by purification of the cerium oxide for regenerating the
abrasive. In the collected cerium oxide which is a solid component
or in the abrasive-containing slurry that contains cerium oxide, a
glass component derived from a polished object and generated in
glass polishing such as silicon dioxide particles are also
included. To separate this glass component, further various
processes are required.
[0047] On the other hand, in the method of the present invention, a
magnesium salt which is a divalent alkali earth metal salt is
selectively interacted with cerium oxide to selectively aggregate
the cerium oxide, whereas a glass component which is not an
abrasive component is hardly aggregated. The method of the present
invention can therefore efficiently separate them. This feature
enables selective separation of high-purity cerium oxide and does
not require a subsequent purification. Thus, the method of the
present invention can simplify a steps) after the separation.
[0048] In the present invention, it is needed to maintain the pH of
the mother liquid of a first abrasive-containing slurry to be in a
predetermined range equal to or less than the pH after the addition
of a magnesium salt, upon the end of adding a magnesium salt to the
separation of an aggregate without adding a pH adjusting agent,
unlike conventional methods. In the present invention, the pH after
the addition of a magnesium salt means the pH right after (upon)
the end of adding a magnesium salt.
[0049] It is also found that the magnesium salt used in the
collecting step is partially absorbed in cerium oxide particles and
thus remains in the regenerated cerium oxide-containing abrasive,
and found that this magnesium salt is bonded to cerium oxide via a
peculiar bond and prevents cerium oxide from becoming too fine
particles in a future use as an abrasive.
BRIEF DESCRIPTION OF DRAWINGS
[0050] [FIG. 1] This is a schematic diagram illustrating a flow
chart of elemental steps of the method of the present invention for
regenerating an abrasive.
[0051] [FIG. 2] This is a schematic diagram illustrating an example
of a flow in a separating and concentrating step B and an abrasive
collecting step C.
[0052] [FIG. 3] This is a schematic diagram illustrating an example
of a particle size adjusting step D using an ultrasonic
disperser.
EMBODIMENTS FOR CARRYING OUT THE INVENTION
[0053] A method for regenerating an abrasive according to an
embodiment of the present invention is a method for regenerating a
cerium oxide-containing abrasive from a used cerium
oxide-containing abrasive, the method including: 1) a slurry
collecting step A in which an abrasive-containing slurry discharged
is collected from an abrasive device; 2) a separating and
concentrating step B in which a magnesium salt is added as an
inorganic salt to the collected abrasive-containing slurry at a
converted pH ranging from 6.5 to less than 10 of a mother liquid at
25.degree. C. so as to aggregate the abrasive selectively and not
to aggregate a non-abrasive component (s) and then separate the
abrasive from the mother liquid and concentrate the abrasive; and
3) an abrasive collecting step C in which the separated and
concentrated abrasive is collected.
[0054] Preferably, the method further includes a particle size
adjusting step D after the abrasive collecting step C. In the
slurry collecting step A, it is preferable to collect a first
abrasive-containing slurry that contains washing water and a second
abrasive-containing slurry that was used, both of which are
discharged from the abrasive device. In the slurry collecting step
A, it is also preferable that the first abrasive-containing slurry
and the second abrasive-containing slurry which were collected in
the slurry collecting step A are mixed to prepare a mother liquid
and thereafter subjected to the separating and concentrating step B
and the abrasive collecting step C, or the first
abrasive-containing slurry and the second abrasive-containing
slurry which were collected in the slurry collecting step A are
separately subjected to the separating and concentrating step B and
the abrasive collecting step C. Preferably, in the abrasive
collecting step C, the abrasive is collected through separation by
decantation utilizing spontaneous sedimentation. In the particle
size adjusting step D, it is preferable that the particle size is
adjusted through adding a dispersing agent to a liquid of the
collected abrasive followed by dispersion using an ultrasonic
disperser or a bead mill disperser. To achieve the effects of the
present invention more sufficiently, the disperser used in the
particle size adjusting step D is preferably an ultrasonic
disperser, and the dispersing agent is preferably a dispersing
agent composed of a poly carboxylic acid-based polymer.
[0055] The present invention, and elements and embodiments thereof
will now be described in detail. Ranges of values expressed with
"(from) A to B" in the following description include the values A
and B as the minimum and maximum values of the ranges.
[0056] <<Method for Regenerating Abrasive>>
[0057] A flow chart of the method of an embodiment of the present
invention for regenerating an abrasive will now be described.
[0058] FIG. 1 is a schematic diagram illustrating a flow chart of
elemental steps of the method of the present invention for
regenerating an abrasive.
[0059] In a polishing process illustrated in FIG. 1, an abrasive
device 1 includes an abrasive surface plate 2 on which an abrasive
cloth F composed of a non-woven cloth, synthetic resin foam or
synthetic leather is adhered. The abrasive surface plate 2 is
rotatable. In polishing, the abrasive surface plate 2 is rotated
while an object 3 to be polished (e.g., glass) is pushed against
the abrasive surface plate 2 with a predetermined pressure force.
Simultaneously, a cerium oxide-containing abrasive liquid 4 (i.e.,
the second abrasive-containing slurry) is supplied through a slurry
nozzle 5 using a pump. The cerium oxide-containing abrasive liquid
4 passes through a flow pass 6 and is then put and pooled in a
slurry tank T.sub.1. The cerium oxide-containing abrasive liquid 4
is repeatedly circulated through the abrasive device 1 and the
slurry tank T.sub.1.
[0060] Washing water 7 is pooled in a washing water tank T.sub.2,
and for washing the abrasive device 1, sprayed through a washing
water-spraying nozzle 8 to a polishing portion. Then, an
abrasive-containing wash liquid 10 (i.e., the first
abrasive-containing slurry) passes through a flow pass 9 using a
pump and is put and pooled in a wash liquid tank T.sub.3. The wash
liquid tank T.sub.3 is used for pooling the wash liquid that was
used in the washing (rinsing). The pooled liquid is continuously
stirred using a stirring blade to avoid sedimentation and
aggregation.
[0061] The abrasive liquid 4 that is pooled in the slurry tank
T.sub.1 and was repeatedly circulated and used (i.e., the second
abrasive-containing slurry) and the wash liquid 10 that is pooled
in the wash liquid tank T.sub.3 (i.e., the first
abrasive-containing slurry) are both contain not only particles of
cerium oxide which is the abrasive but also a non-abrasive
component(s) removed from the polished object 3 (e.g., glass) which
is polished in the polishing process.
[0062] Subsequently, the abrasive liquid 4 (the second
abrasive-containing slurry) and the wash liquid 10 (the first
abrasive-containing slurry) are mixed and then collected, or are
separately collected. This step is defined as the slurry collecting
step A.
[0063] Thereafter, to a mixture of or each of the abrasive liquid 4
(the second abrasive-containing slurry) and the wash liquid 10 (the
first abrasive-containing slurry) which were collected in the
slurry collecting step A (the mixture of these liquids is called a
mother liquid, and each liquid is called a mother liquid), a
divalent alkali earth metal salt is added as an inorganic salt
without adding any pH adjusting agent under the condition that
aggregates the abrasive selectively and does not aggregate a
non-abrasive component (s) (e.g., glass powder) to separate only
the abrasive from the mother liquid and concentrate the abrasive
(the separating and concentrating step B).
[0064] Then, liquid-solid separation is conducted utilizing
spontaneous sedimentation. No forcible way is employed in this
separation to separate the mother liquid into a supernatant
containing the non-abrasive component (s) etc. and a concentrate
containing cerium oxide sediment. Thereafter, the supernatant is
disposed by decantation, e.g., tilting of the container, or by
putting a discharging pipe to reach near the interface between the
supernatant and the concentrate in the container in which the
separation is conducted, so as to discharge only the supernatant
from the container and collect the abrasive (the abrasive
collecting step C).
[0065] In the separated cerium oxide-containing concentrate,
particles of cerium oxide form aggregates (i.e., secondary
particles) together with the inorganic salt. In order to break the
aggregates into almost pure primary particles, water and a
dispersing agent are added, and a dispersing device is used to
obtain particles with desired sizes (the particle size adjusting
step D).
[0066] The regenerated abrasive of high-quality can be thus
obtained in such a simple manner.
[0067] Details of the method of the embodiment of the present
invention for regenerating an abrasive and techniques for the
method will now be described.
[0068] [Abrasive]
[0069] Generally, fine particles of Bengala (.alpha.
Fe.sub.2O.sub.3), cerium oxide, aluminum oxide, manganese oxide
and/or zirconium oxide, or colloidal silica is dispersed as an
abrasive in water or oil to form a slurry, and it is used for
polishing optical glasses, semiconductor substrates and the like.
On the other hand, an abrasive used in the present invention is
mainly composed of cerium oxide. This abrasive is applicable to
Chemical Mechanical Polishing (CMP). CMP utilizes mechanical and
chemical actions and achieves sufficient speed and highly fine
flatness in polishing the surface of a semiconductor substrate or a
glass.
[0070] Actually, the cerium oxide widely used as an abrasive is not
pure cerium oxide but is so-called bastnaesite which is prepared by
sintering a mineral ore rich in rare earth elements and crashing
the mineral ore. In this cerium oxide, cerium oxide is present as a
main component. In addition, other rare earth elements such as
lanthanum, neodymium, praseodymium and the like are also contained
in the cerium oxide. Fluorides of them may be contained in the
cerium oxide in addition to oxides of them.
[0071] The composition and shape of cerium oxide used in the
present invention is not particularly limited. A commercially
available cerium oxide can be used as the abrasive in the present
invention. Preferably, the concentration of cerium oxide is 50% by
mass or more in cerium oxide to achieve the effects of the present
invention more sufficiently.
[0072] [Polishing Process]
[0073] The abrasive is used in the following way (polishing
process). The present invention is a method for efficiently
regenerating an abrasive from a used abrasive that is used as
described below.
[0074] Taking polishing of a glass substrate as an example, a
polishing process is normally composed of preparing an
abrasive-containing slurry, polishing and washing, as illustrated
in FIG. 1.
[0075] (1) Preparation of Abrasive-Containing Slurry
[0076] Powder of an abrasive mainly composed of cerium oxide is
added in an amount of 1 to 40% by mass to a solvent such as water
and then dispersed in the solvent to obtain an abrasive-containing
slurry. This abrasive-containing slurry is circulated through an
abrasive device and used. The cerium oxide powder (fine particles)
used as the abrasive has an average size ranging from several dozen
nanometers to several micrometers.
[0077] By adding a dispersing agent and the like, aggregation of
the cerium oxide particles can be prevented. Preferably, dispersing
state is maintained by stirring using a stirrer or the like. In
general, it is preferable that a tank used for pooling an
abrasive-containing slurry is arranged next to an abrasive device,
dispersing state is maintained using a stirrer or the like, and the
abrasive-containing slurry is supplied to the abrasive device and
circulated through the abrasive device using a supplying pump.
[0078] (2) Polishing
[0079] As illustrated in FIG. 1, a glass substrate is polished by
bringing the glass substrate into contact with the abrasive pad
(abrasive cloth) and moving the glass substrate and the abrasive
pad relative to each other applying pressure force with the
supplementation of the abrasive-containing slurry to the contacting
portion.
[0080] (3) Washing
[0081] When the polishing is finished, a large quantity of the
abrasive is present on the glass substrate and the abrasive device.
Thus, water or the like is supplied in place of the
abrasive-containing slurry after the polishing to wash the abrasive
to remove it from the glass substrate and the abrasive device.
Then, the washing water that contains the abrasive is discharged to
the outside of the polishing system.
[0082] As a result of the washing, a certain amount of the abrasive
is discharged to the outside of the polishing system, and thus the
amount of the abrasive in the polishing system is reduced. To make
up for this reduction, a fresh abrasive-containing slurry is newly
supplied to the slurry tank T.sub.1. The addition may be conducted
once every polishing process or once every predetermined times of
repeated polishing process. Preferably, the abrasive is in a
well-dispersed state in the solvent in the supplementation.
[0083] [Used Abrasive-Containing Slurry]
[0084] In the present invention, the used abrasive-containing
slurry is the abrasive-containing slurry discharged to the outside
of the system including the abrasive device and the tank used for
the abrasive-containing slurry, and is categorized into the
following two types.
[0085] One is the first abrasive-containing slurry which contains
the washing water discharged in the washing process (a rinse
slurry), and the other is the second abrasive-containing slurry
that was used and is pooled in the slurry tank T.sub.1 (a
life-ended slurry). In the present invention, they are called the
first abrasive-containing slurry and the second abrasive-containing
slurry, respectively. The present invention is preferably applied
to both of the first abrasive-containing slurry and the second
abrasive-containing slurry, but may be applied to either of
them.
[0086] The first abrasive-containing slurry which contains the
washing water is characterized by the following two features.
[0087] 1) This is discharged in the washing. Thus, this slurry
contains a large amount of the washing water and the concentration
of the abrasive in this slurry is lower than that of the slurry in
the tank.
[0088] 2) The glass component which was present on the abrasive
cloth or the like is included in this slurry as a result of the
washing.
[0089] On the other hand, the second abrasive-containing slurry is
characterized in that the concentration of the glass component is
higher than that of a fresh abrasive-containing slurry.
[0090] [Regeneration of Abrasive Containing Cerium Oxide]
[0091] In the present invention, the method for regenerating the
abrasive and producing the regenerated cerium oxide-containing
abrasive is mainly composed of four steps, namely, the slurry
collecting step A, the separating and concentrating step B, the
abrasive collecting step C and the particle size adjusting step
D.
[0092] (1: Slurry Collecting Step A)
[0093] In this step, the abrasive-containing slurry discharged from
the system composed of the abrasive device and the slurry tank is
collected. The slurry to be collected in this step is categorized
into the first abrasive-containing slurry which contains the
washing water and the second abrasive-containing slurry which was
used.
[0094] Generally, the concentration of the cerium oxide-containing
abrasive in the collected abrasive-containing slurry is 0.1 to 40%
by mass.
[0095] The collected slurry may be immediately subjected to the
separating step or may be pooled to obtain a certain amount of the
collected slurry. In each case, it is preferable to continuously
stir the collected slurry to maintain the dispersing state.
[0096] In the present invention, the first abrasive-containing
slurry and the second abrasive-containing slurry collected in the
slurry collecting step A may be mixed with each other to prepare
the mother liquid and then subjected to the separating and
concentrating step B and the abrasive collecting step C. Otherwise,
the first abrasive-containing slurry and the second
abrasive-containing slurry collected in the slurry collecting step
A may be separately subjected to the separating and concentrating
step B and the abrasive collecting step C as the mother liquids
independent from each other.
[0097] (2: Separating and Concentrating Step B)
[0098] Each collected slurry which was used contains a glass
component derived from the polished object. The concentration of
the abrasive is decreased due to influx of the washing water. To
use the slurry again for the polishing, the glass component is
required to be separated, and the abrasive component is required to
be concentrated.
[0099] In the separating and concentrating step B of the present
invention, a magnesium salt which is a divalent alkali earth metal
salt is added as an inorganic salt to the collected slurry (mother
liquid) which was collected in the slurry collecting step A at a
converted pH ranging from 6.5 to less than 10 of the mother liquid
so as to aggregate only the abrasive and so as not to aggregate the
non-abrasive component (s). Hence, the abrasive component mainly
composed of cerium oxide is aggregated, and then sedimentation
occurs. Thereafter, the aggregate is separated from the supernatant
which contains most of the glass component. Thus, this step enables
both of the separation of the cerium oxide component from the glass
component and the concentrating in the abrasive-containing
slurry.
[0100] Specific operations will now be described with reference to
FIG. 2.
[0101] FIG. 2 is a schematic diagram illustrating an example of a
flow in a separating and concentrating step B and an abrasive
collecting step C.
[0102] As a step (B-1), the abrasive-containing slurry (mother
liquid) 13 which is collected in the previous step, i.e., the
slurry collecting step A is poured into a conditioning container 14
equipped with a stirrer 15. Thereafter, as a step (B-2), a
magnesium salt which is a divalent alkali earth metal salt is added
as an inorganic salt from a adding flask 16 to the
abrasive-containing slurry (mother liquid) 13 being stirred at a
converted pH ranging from 6.5 to less than 10 of the mother liquid
at 25.degree. C. Subsequently, in a step (B-3), the cerium oxide
particles in the abrasive-containing slurry (mother liquid) 13 is
selectively aggregated as a result of the addition of the inorganic
salt, and then sedimentation of the aggregate occurs to form an
aggregate 18. In a supernatant 17 from which the separated sediment
of the cerium oxide is removed contains a non-abrasive component(s)
such as a glass component. The abrasive and non-abrasive components
are thus separated from each other.
[0103] <Divalent Alkali Earth Metal Salt>
[0104] In the present invention, the inorganic salt used for
aggregating the cerium oxide is a divalent alkali earth metal
salt.
[0105] Examples of the divalent alkali earth metal salt used in the
present invention include calcium salts, barium salts, beryllium
salts and magnesium salts. Among them, magnesium salts are
preferable to achieve the effects of the present invention more
sufficiently.
[0106] Any electrolyte magnesium salt may be used in the present
invention without particular limitation. In terms of high
solubility in water, magnesium chloride, magnesium bromide,
magnesium iodide, magnesium sulfate and magnesium acetate are
preferable. In terms of a small change in pH and easiness of
treating the sediment of the abrasive and the waste liquid,
magnesium chloride and magnesium sulfate are particularly
preferable.
[0107] <Method for Adding Divalent Alkali Earth Metal
Salt>
[0108] A method for adding the divalent alkali earth metal salt
will now be described.
[0109] a) Concentration of Magnesium Salt
[0110] Powder of the magnesium salt may be directly added to the
collected slurry, or the magnesium salt may be dissolved in a
solvent such as water and then added to the abrasive-containing
slurry. It is preferable that the magnesium salt is dissolved in a
solvent and then added to the abrasive-containing slurry to obtain
homogeneous concentration in the slurry after the addition.
[0111] The concentration is preferably 0.5 to 50% by mass in an
aqueous solution. To suppress a change in pH of the system and
achieve more efficient separation of the glass component, the
concentration is preferably 10 to 40% by mass.
[0112] b) Temperature in Adding Magnesium Salt
[0113] The temperature when the magnesium salt is added may be in
the range from the freezing temperature of the collected
abrasive-containing slurry to 90.degree. C. To efficiently separate
the glass component, the temperature is preferably 10 to 40.degree.
C., and more preferably 15 to 35.degree. C.
[0114] c) Speed of Adding Magnesium Salt
[0115] Speed of adding the magnesium salt is preferably adjusted so
that the concentration of the added magnesium salt in the collected
abrasive-containing slurry is not largely changed immediately and
the added magnesium salt is homogeneously present in the collected
abrasive-containing slurry. The amount of the added magnesium salt
per minute is preferably 20% by mass or less, more preferably 10%
by mass or less, per the total amount of the magnesium salt to be
added.
[0116] d) pH Value after Addition of Magnesium Salt
[0117] In the separating and concentrating step B of the present
invention, the magnesium salt is added and then separation and
concentration is conducted at a converted pH ranging from 6.5 to
less than 10 of the mother liquid at 25.degree. C. Generally, the
collected abrasive-containing slurry exhibits alkalinity and its pH
ranges from 8 to less than 10 because of the presence of the glass
component. Thus, it is not needed to adjust the pH of the collected
abrasive-containing slurry in advance.
[0118] In the present invention, the pH value is obtained from the
measurement at 25.degree. C. using the Lacombe tester bench pH
meter (pH1500, manufactured by AS ONE CORPORATION).
[0119] In the present invention, the pH value is equal to or less
than the pH value after the addition of the magnesium salt upon the
addition of the magnesium salt to the separation of the aggregate.
In the present invention, the pH value after the addition of the
magnesium salt is the pH value right after (upon) the end of adding
the magnesium salt.
[0120] Until the end of separating the aggregate, the pH is equal
to or less than the pH value after the addition of the magnesium
salt. Specifically, the pH ranges from 6.5 to less than 10, which
pH is a converted pH at 25.degree. C. To maintain the pH value
under 10, the glass component in the waste liquid can be prevented
from being aggregated, and thus the purity of the collected cerium
oxide can increase.
[0121] The minimum value of the pH after the addition of the
magnesium salt is 6.5 or more considering decrease in the purity
due to a pH adjusting agent and handleability.
[0122] e) Stirring after Addition of Magnesium Salt
[0123] After the addition of the magnesium salt, the stirring is
continued for preferably 10 minutes or more, and more preferably 30
minutes or more. Upon the addition of the magnesium salt, the
aggregation of the abrasive particles starts. The continuous
stirring makes the aggregation state homogeneous in the liquid and
reduces the particle size distribution, which makes the following
separation easy.
[0124] (3: Abrasive Collecting Step C)
[0125] In the separating and concentrating step B, the aggregate 18
is separated from the supernatant 17 which contains the glass
component, and then the aggregate 18 is collected, as illustrated
in FIG. 2.
[0126] a) Method for Separating Aggregate of Abrasive
[0127] A commonly-used method for separating an aggregate can be
used as the method for separating the aggregate of the abrasive
which is obtained by adding the magnesium salt from the
supernatant. For example, spontaneous sedimentation can be utilized
to remove only the supernatant for separating the supernatant. A
method utilizing physical actions such as a method using a
centrifugal separator can also be employable. In terms of the
purity of the regenerated cerium oxide-containing abrasive, a
method utilizing spontaneous sedimentation is preferable.
[0128] In the sedimentation state, its specific weight is higher
than that of the collected slurry because the supernatant is
separated, and thus the cerium oxide is concentrated. The
concentration of the cerium oxide in this concentrated slurry is
higher than that of the collected slurry.
[0129] For example, the separation of the aggregate of the abrasive
from the supernatant can be conducted as follows. As illustrated in
FIG. 2, the concentrate 18 which contains the cerium oxide settled
at the bottom is separated from the supernatant 17 which contains
the non-abrasive component(s) utilizing spontaneous sedimentation
as the step (B-3). Thereafter, the discharging pipe 19 is put in
the container 14 to reach near the interface between the
supernatant 17 and the concentrate 18, and then only the
supernatant 17 is discharged to the outside of the container using
the pump 20, as the step (C-1). Subsequently, the concentrate 18
which contains the abrasive is collected as the step (C-2).
[0130] (4: Particle Size Adjusting Step D)
[0131] In the method of the present invention for regenerating an
abrasive, the particle size distribution of particles of the cerium
oxide is adjusted as a final step to make the used abrasive
collected through the above steps reusable.
[0132] The collected aggregate of the cerium oxide obtained by
adding the magnesium salt or the like is composed of lumps of
secondary particles. Thus, for the purpose of the reuse, it is
preferable to conduct the particle size adjusting step D to cause
re-dispersion through breaking the aggregate into pure particles
(i.e., primary particles) as a final step.
[0133] In the particle size adjusting step D, the aggregate of the
abrasive generated in the separating and concentrating step B is
re-dispersed to adjust the particle size distribution to be
equivalent to that in the un-treated abrasive slurry.
[0134] Examples of the method for re-dispersing the aggregate of
the abrasive particles are as follows: a) water is added to lower
the concentration of the magnesium ion in the liquid; b) a
metal-separating agent (or a dispersing agent) is added to lower
the concentration of the magnesium ion on the abrasive; and c) the
aggregate of the abrasive particles is cracked using a dispersing
device or the like.
[0135] One of these methods can be used alone, or two or more of
them may be used in combination. Preferably, any two of the methods
a), b) and c) are used in combination. More preferably, all of the
methods a), b) and c) are used in combination.
[0136] In the case of adding water, the amount of water to be added
is adjusted according to the volume of the concentrated slurry.
Generally, the amount of water is 5 to 50% by volume of the
concentrated slurry, and preferably 10 to 40% by volume of the
concentrated slurry.
[0137] Preferable examples of the metal-separating agent
(dispersing agent) include agents composed of a poly-carboxylic
acid-based polymer. An acrylic acid-maleic acid copolymer is
particularly preferable. Specifically, LITY A-550 (manufactured by
Lion Corporation) is given as an example. The amount of the
metal-separating agent (dispersing agent) to be added to the
concentrated slurry is preferably 0.01 to 5% by volume.
[0138] Examples of the dispersing device include ultrasonic
dispersers and media mills such as sand mills and bead mills.
Ultrasonic dispersers are particularly preferable.
[0139] For example, ultrasonic dispersers are available from SMT
Corporation, Ginsen Corporation, TAITEC Corporation, BRANSON,
Kinematica AG, and NISSEI Corporation. Examples include UDU-1 and
UH-600MC manufactured by SMT Corporation, GSD600CVP manufactured by
Ginsen Corporation and RUS600TCVP manufactured by NISSEI
Corporation. The frequency of ultrasonic is not particularly
limited.
[0140] Examples of circulating type devices that conduct mechanical
stirring and ultrasonic dispersion simultaneously include, but are
not limited to, UDU-1 and UH-600MC manufactured by SMT Corporation,
GSD600CVP and GSD1200RCVP manufactured by Ginsen Corporation and
RUS600TCVP manufactured by NISSEI Corporation.
[0141] FIG. 3 is a schematic diagram illustrating an example of the
particle size adjusting step D using an ultrasonic disperser.
[0142] As illustrated in FIG. 3, to the aggregate obtained in the
abrasive collecting step C in a conditioning container 21, a) water
is added to lower the concentration of the magnesium salt in the
liquid to prepare a cerium oxide-dispersing liquid 22 and pools it
in the conditioning container 21. Then, the metal-separating agent
(dispersing agent composed of a polymer) described in the above b)
is added from 23 to the cerium oxide-dispersing liquid 22 being
stirred using a stirrer 15. Thereafter, the resulting liquid is
passed through a flow pass 24 using a pump 20 to an ultrasonic
dispersing device 26, and is then subjected to dispersion to break
the aggregated particles of the cerium oxide. Subsequently, the
particle size distribution is monitored using a particle size
measuring device 27 provided in the downstream of the ultrasonic
disperser 26. Upon confirming that the particle size distribution
has reached a desired value, a three-way valve 25 is controlled,
and the resulting cerium oxide-dispersing liquid 22 is then passed
through a flow pass 29. The regenerated abrasive can be thus
obtained.
[0143] Preferably, a change with time of the particle size
distribution obtained in this step is small, and a change in the
particle size after one day has passed is small.
[0144] [Regenerated Abrasive Containing Cerium Oxide]
[0145] In the present invention, the particle size distribution of
the regenerated abrasive containing the cerium oxide obtained
through the particle size adjusting step D as a final product is
difficult to change with time. The concentration is higher than
that after the collection. The concentration of magnesium is
preferably ranges from 0.0005 to 0.08% by mass, and the
concentration (s) of the other component (s) are preferably 1.0% by
mass or less in total.
[0146] The regenerated abrasive obtained by the method for
regenerating an abrasive contains a slight amount of the divalent
alkali earth metal salt such as a magnesium salt. Generation of too
fine particles in the use of the regenerated abrasive can therefore
be suppressed and the regenerated abrasive can polish an object
equivalently to a fresh abrasive.
Example
[0147] The present invention will now be described in detail with
reference to Examples, but the present invention is not limited
thereto. The percent sign "%" in the following description means "%
by mass" unless described otherwise.
[0148] <<Preparation of Regenerated Abrasive>>
[0149] [Preparation of Regenerated Abrasive 1: Present
Invention]
[0150] A regenerated abrasive 1 was prepared through the following
steps. Regeneration of an abrasive was conducted at 25.degree. C.
and 55% RH unless described otherwise. In the regeneration, the
temperature of the liquid was also 25.degree. C.
[0151] 1) Slurry Collecting Step A
[0152] After a glass substrate for a hard disc was polished as a
polishing process illustrated in FIG. 1, 210 liters of the first
abrasive-containing slurry which contained the washing water and 30
liters of the second abrasive-containing slurry which had been used
were collected, and then mixed to obtain 240 liters of the
collected slurry. The specific weight of this collected slurry was
1.03, and the collected slurry contained 8.5 kg of the cerium
oxide.
[0153] 2) Separating and Concentrating Step B
[0154] Subsequently, 2.5 liters of 10-% aqueous solution by mass of
magnesium chloride was added spending 10 minutes while the
collected slurry was stirred so as to avoid sedimentation of the
cerium oxide. The converted pH value right after (upon) the end of
adding magnesium chloride at 25.degree. C. was 8.60.
[0155] 3) Abrasive Collecting Step C
[0156] The above stirring was continued for 30 minutes, and then
the resulting slurry was left to stand for 1.5 hours to separate
the aggregate 18 and let it settle out from the supernatant 17
utilizing spontaneous sedimentation. After 1.5 hours had passed,
the supernatant 17 was discharged using the discharging pump 20 in
accordance with the step (C-1) in FIG. 2, and the aggregate 18 was
separated and collected in accordance with the step (C-2) in FIG.
2. The volume of the collected aggregate was 60 liters.
[0157] 4) Particle Size Adjusting Step D (Dispersing Step)
[0158] To the separated aggregate, 12 liters of water was added. In
addition, 300 g of POLITY A-550 (Manufactured by Lion Corporation)
was added as the metal-separating agent (dispersing agent composed
of a polymer) to the separated aggregate, followed by stirring for
30 minutes. Thereafter, the aggregate was broken and dispersed
using an ultrasonic disperser as illustrated in FIG. 3.
[0159] After the dispersion was completed, then filtration was
conducted using a membrane filter with a pore size of 10 .mu.m to
obtain the regenerated cerium oxide-containing abrasive 1. The
concentration of the cerium oxide was 8.7% by mass, and the
particle size D90 was less than 2.0 .mu.m. The concentration of
magnesium in the regenerated abrasive was 0.03% by mass.
[0160] [Preparation of Regenerated Abrasive 2: Present
Invention]
[0161] A regenerated abrasive 2 was prepared by the same way as the
regenerated abrasive 1 was prepared except that magnesium sulfate
was used in place of magnesium chloride as the inorganic salt used
in 2) the separating and concentrating step B.
[0162] [Preparation of Regenerated Abrasive 3: Present
Invention]
[0163] A regenerated abrasive 3 was prepared by the same way as the
regenerated abrasive 1 was prepared except that a bead mill
disperser was used in place of the ultrasonic disperser as the
dispersing device in 4) the particle size adjusting step D
(dispersing step).
[0164] [Preparation of Regenerated Abrasive 4: Comparative
Example]
[0165] A regenerated abrasive 4 was prepared by the same way as the
regenerated abrasive 1 was prepared except that potassium carbonate
was used in place of magnesium chloride as the inorganic salt used
in 2) the separating and concentrating step B.
[0166] [Preparation of Regenerated Abrasive 5: Comparative
Example]
[0167] A regenerated abrasive 5 was prepared by the same way as the
regenerated abrasive 1 was prepared except that the pH of the
collected slurry was adjusted to 10.10 using potassium hydroxide
after adding magnesium chloride as the inorganic salt to the
collected slurry in 2) the separating and concentrating step B.
[0168] [Preparation of Regenerated Abrasive 6: Comparative
Example]
[0169] A regenerated abrasive 6 was prepared by the same way as the
regenerated abrasive 1 was prepared except that the pH was adjusted
to 10.80 using potassium hydroxide after adding magnesium chloride
as the inorganic salt to the collected slurry in 2) the separating
and concentrating step B.
[0170] [Preparation of Regenerated Abrasive 7: Present
Invention]
[0171] A regenerated abrasive 7 was prepared by the same way as the
regenerated abrasive 1 was prepared except that a 25% aqueous
solution by mass of magnesium sulfate was added in place of the 10%
aqueous solution by mass of magnesium chloride as the inorganic
salt in 2) the separating and concentrating step B, and the slurry
was put into an in-line ultrasonic disperser (UIP2000, manufactured
by Hielscher GmBH) before subjected to the filtration using the
membrane filter with a pore size of 10 .mu.m.
[0172] The concentration of the cerium oxide in the regenerated
abrasive 7 was 9.0% by mass, and the particle size D90 was less
than 2.0 .mu.m. The concentration of magnesium was 0.04% by mass.
The ratio of collecting the cerium oxide was 83%.
[0173] [Preparation of Regenerated Abrasives 8 to 11]
[0174] In preparing regenerated abrasives 8 to 11, sodium chloride
(regenerated abrasive 8), sodium sulfate (regenerated abrasive 9),
potassium chloride (regenerated abrasive 10), and calcium chloride
(regenerated abrasive 11) were used, respectively, in place of the
organic salt in 2) the separating and concentrating step B under
the condition same as the condition in the step B in the
preparation of the regenerated abrasive 1. In the case where sodium
chloride was added and the case where sodium sulfate was added, no
aggregation occurred after the continuous stirring for 30 minutes
and the subsequent standing for 1.5 hours. In the case where
potassium chloride was used and the case where calcium chloride was
used, the aggregation speed was low. In addition, the glass
component was aggregated together with the abrasive component, and
thus the glass component was not separated.
[0175] <<Evaluation of Regenerated Abrasive>>
[0176] [Evaluation for Purity of Regenerated Abrasive: Evaluation
for Separability from Glass Component]
[0177] In the preparation of the above regenerated abrasives 1 to
5, samples were taken from the collected slurries before the
addition of the inorganic salt in 2) the separating and
concentrating step B and from the supernatants after the standing
and the separation. The taken samples were then subjected to
component analysis using an ICP Atomic Emission spectrometer. If
the concentration of cerium in the sample from the supernatant was
lower than that in the sample from the un-treated collected slurry
and the concentrations of silicon did not differ from each other,
it is concluded that only the cerium oxide particles settled out
and the glass particles which are not derived from the abrasive did
not settle out and remained in the supernatant. On the other hand,
if the concentration of cerium and the concentration of silicon in
the sample from the supernatant are both lower than those in the
sample from the un-treated collected slurry, it is concluded that
the cerium oxide particles and the glass particles both settled out
and thus they are not sufficiently separated from each other.
[0178] (Component Analysis using ICP Atomic Emission
Spectrometry)
[0179] The concentrations of the cerium component and the glass
component (Si) in each sample from the separated supernatant were
measured using ICP Atomic Emission Spectrometry, and compared to
those in each sample from the untreated used slurry (i.e., the
slurry to which no additive was added). Specific steps are
described below.
[0180] <Preparation of Sample Solution A>
[0181] (a) 1 ml of a sample was taken from the un-treated collected
slurry or the supernatant being stirred by a stirrer
[0182] (b) 5 ml of hydrofluoric acid for atomic absorption was
added to the sample
[0183] (c) silica was eluted by ultrasonic dispersion
[0184] (d) the sample was left to stand at room temperature for 30
minutes
[0185] (e) ultrapure water was added to the sample to obtain a
volume of 50 ml
[0186] Each sample liquid prepared through the above steps is
called the sample liquid A.
[0187] <Quantification of Si and Mg>
[0188] (a) the sample liquid A was filtrated using a membrane
filter (hydrophilic PTFE)
[0189] (b) the filtrate was subjected to measurement using an
Inductivity Coupled Plasma Atomic Emission spectrometer
(ICP-AES)
[0190] (c) Si was quantified through a standard addition method,
and Mg was quantified through a calibration-curve method using
matrix matching
[0191] <Quantification of Cerium>
[0192] (a) 5 ml of a sample was taken from the sample liquid in a
well dispersing state
[0193] (b) 5 ml of high-purity sulfuric acid was added to the above
taken sample
[0194] (c) ultrapure water was added to the resulting sample to
obtain a volume of 50 ml
[0195] (d) the resulting sample was diluted as needed and subjected
to measurement using ICP-AES
[0196] (e) cerium was quantified through a calibration-curve method
using matrix matching
[0197] <ICP Atomic Emission spectrometer>
[0198] An ICP-AES manufactured by SII nanotechnology Inc. was
used.
[0199] Results from the measurements are shown in Table 1.
TABLE-US-00001 TABLE 1 pH of Dispersing slutty device at in the end
particle Analysis of supernatant of adding size using ICP
Regenerated Inorganic inorganic adjusting Si Ce abrasive No. salt
salt step concentration concentration Note 1 Magnesium 8.60
Ultrasonic 978 41 Present Chloride Disperser Inention 2 Magiesium
8.94 Ultrasonic 918 50 Present Sulfate Disperser Inention 3
Magnesium 8.60 Bead mill 970 43 Present Chloride disperser Inention
4 Pottasium 9.86 Ultrasonic 186 30 Comparative Carbonate Disperser
Example 5 Magnesium 10.10 Ultrasonic 91 26 Comparative Chloride
Disperser Example 6 Magnesium 10.80 Ultrasonic 61 18 Comparative
Chloride Disperser Example Reference: Un-treated slurry 1060
5400
[0200] As evident from the results shown in Table 1, the method of
the present invention for regenerating an abrasive is excellent in
separability of the cerium oxide (i.e., the abrasive) from the
glass component (i.e., the non-abrasive component) in the
precipitating and separating and thus can provide a higher-purity
regenerated abrasive, compared to the methods of Comparative
Examples for regenerating an abrasive.
INDUSTRIAL APPLICABILITY
[0201] The method of the present invention for regenerating an
abrasive can be suitably applied to regenerate an abrasive used in
fine polishing in a finishing process of optical glasses and
crystal oscillators, because the method of the present invention
can efficiently collect cerium oxide and can provide a regenerated
abrasive in a simple manner.
DESCRIPTION OF REFERENCE SIGNS
[0202] 1 Abrasive device [0203] 2 Abrasive surface plate [0204] 3
Polished object [0205] 4 Abrasive liquid [0206] 5 Slurry nozzle
[0207] 7 Washing water [0208] 8 Washing water-spraying nozzle
[0209] 10 Abrasive-containing wash liquid [0210] 13
Abrasive-containing slurry (Mother liquid) [0211] 14, 21
Conditioning container [0212] 15 Stirrer [0213] 16 Adding flask
[0214] 17 Supernatant [0215] 18 Concentrate [0216] 19 Discharging
pipe [0217] 20 Pump [0218] 25 Three-way valve [0219] 27 Particle
size measuring device [0220] F Abrasive cloth [0221] T.sub.1 Slurry
tank [0222] T.sub.2 Washing water tank [0223] T.sub.3 Wash liquid
tank
* * * * *